1. Field of the Invention
The present invention relates to a combustion-engined setting tool for driving fastening elements such as nails, bolts, pins in an object and including a combustion chamber, a fuel source, a fuel conduit connecting the fuel source with the combustion chamber for feeding fuel thereinto, and at least one metering device for metering a predetermined amount of fuel for effecting a setting process and including at least one metering chamber having an adjustable volume.
2. Description of the Prior Art
Combustion-engined setting tools of the type described above can operate with a gaseous or liquid fuel that is combusted in the combustion chamber generating pressure for driving the drive piston which drives a fastening element in.
Generally, the problem with combustion consists in admixing, to a proportional amount of fuel for each operational cycle, a corresponding amount of air or oxygen used as an oxidation medium. The amount of oxygen, which is available for use in combustion, depends very much on the surrounding temperature, air pressure, and air humidity. The necessary amount of fuel varies greatly with changes in the above-listed parameters, up to 40% in an extreme case. These variations of the amount of fuel unfavorably influence the combustion of the air-fuel mixture when the fuel-air mixture contains too much or too little fuel. Therefore, it is desirable to adapt the used amount of fuel to the respective environmental conditions. In order to achieve an optimal combustion, it is further desirable to inject the fuel into the combustion chamber with as high a speed as possible.
European Publication EP-1 254 745 A2 discloses a setting tool of the type discussed above and having a metering valve in which the volume of the metering chamber is adjusted with a spindle projecting into the metering chamber. For changing and preliminary setting the inner volume of the metering chamber, the spindle is displaced into the metering chamber to a greater or lesser degree. The displacement of the spindle is effected manually by screwing the spindle in or out of the metering chamber. The feeding of fuel to the combustion chamber is effected through an outlet valve under the own pressure of the fuel filling the metering chamber.
European Patent EP-0 597 241 B1 disclosed a combustion-engined setting tool in which a metering device is used for feeding fuel from a fuel source to a combustion chamber. The metering device includes a normally closed solenoid valve. The actuation of the valve is effected electronically and is controlled by a switching circuit. The switching circuit responds to actuation of a switch and opens the valve in a predetermined time interval to provide for flow of fuel from the fuel source to the combustion chamber.
The drawback of the setting tool of EP-0 597 241 B1 consists in that with variations of the pressure in the fuel source the flow velocity of the fuel varies and can result in a non-exact amount of fuel fed to the combustion chamber. The flow of fuel into the combustion chamber takes place under the fuel own pressure.
German Publication DE-42 43 617 A1 discloses a setting tool in which in an operational cycle, a gas inlet valve opens mechanically, and fuel from a fuel source is fed into a storage chamber which communicates with the surrounding air. This communication provides for a pressure and, if necessary, temperature equalization with the surrounding air, whereby a proper air-fuel mixture is fed into the combustion chamber. The fuel is fed from the storage chamber and to the combustion chamber at a predetermined time.
The drawback of the setting tool of DE-42 43 617 A1 consists in that the communication with the surrounding air can cause loss of fuel. Further, the pressure in the metering chamber cannot be controlled.
The object of the present invention is to provide a setting tool of the type described above in which the drawbacks of the prior art tools are eliminated, and an exact metering of full is insured.
Another object of the present invention is to provide a setting tool of the type described above and in which a high setting energy is achieved.